Alternate fuels have been developed to mitigate the rising prices of conventional fuels and for reducing exhaust emissions. For example, natural gas has been recognized as attractive alternative fuels. For automotive applications, natural gas or petroleum gas may be compressed and stored as a liquid (liquefied petroleum gas, or LPG) in cylinders at saturation or higher pressure. The fuel system in such automotive applications may include various components, such as valves and pressure regulators, to ensure correct flow of the fuel, and enable the gaseous fuel to be provided at lower pressures to an engine combustion chamber. In some vehicle systems, the fuel line may be charged with liquid fuel tank pressure before an engine start is initiated. For example, such a “pre-priming” process may be initiated when the driver's door is opened (“door ajar pre-prime”) so that the priming is completed before the driver turns the ignition on. As such, this allows engine start times to be reduced.
However the inventors herein have identified potential issues with such systems. As one example, if there is a leak or breach in the fuel system, the driver may not be able to terminate the pre-priming operation. Specifically, in fuel systems where the priming is initiated after the ignition is turned on, the driver may turn off the ignition, and consequently the priming, if a leak is detected. However, in systems where the pre-priming is automatically initiated, the process may not be terminated until it has run the course. As such, this may lead to degraded engine performance during the subsequent restart due to improper priming.
Thus, in one example, some of the above issues may be addressed by a method for an engine operating on a gaseous fuel comprising, indicating fuel system degradation based on a change in each of a fuel rail pressure and a fuel tank pressure over a duration while the engine is shutdown. In response to the indication, the method further includes disabling pre-priming on a subsequent engine restart. In this way, sufficient pre-priming may be better enabled.
In one example, an engine may be operated with a gaseous fuel, such as LPG, which is delivered to the engine from a dedicated fuel system. During an engine shutdown condition, an electronic controller of the engine system may be temporarily enabled or “woken up” to perform one or more leak detection routines. The diagnostic routines may be performed to identify the presence of gross leaks as well as small leaks in the fuel system. For example, the controller may be enabled for a first, shorter duration while the engine is shutdown and a change in fuel tank pressure and fuel rail pressure may be monitored. If a pressure differential between the fuel rail pressure and the fuel tank pressure is lower than a threshold after the short duration, a gross leak in the fuel system may be determined. The controller may also be enabled for a second, longer duration while the engine is shutdown and a change in fuel rail pressure may be monitored. If the fuel rail pressure decreases towards barometric pressure, a small leak in the fuel system may be determined.
If no fuel system degradation is determined, then a pre-priming operation may be enabled on a subsequent engine restart. Therein, in response to a vehicle operator door being opened, and in anticipation of an imminent engine restart request, a fuel pump may be operated to prime the fuel rail. In comparison, if fuel system degradation is identified, the pre-priming operation may be disabled. Therein, the fuel rail may be primed only after a request for engine restart is received from the operator. Additionally, the priming may be performed for a longer duration in the absence of accurate fuel rail pressure data to preclude insufficient fuel rail priming.
It will be appreciated that the gaseous fuel referred to herein is a fuel that is gaseous at atmosphere conditions but may be in liquid form while at high pressure (specifically, above saturation pressure) in the fuel system. That is, the fuel may be in liquid form until it is injected.
In this way, engine startability may be improved when operating with a gaseous fuel, even in the presence of fuel system leaks. By disabling pre-priming in response to the presence of a fuel system leak, issues related to insufficient fuel rail priming may be reduced. In addition, by enabling leak detection to be performed during engine shutdown conditions, a more accurate indication of fuel system degradation may be attained. Overall, engine performance may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.